Isotopic ecology of coyotes from scat and road kill carcasses: A complementary approach to feeding experiments

Scat is frequently used to study animal diets because it is easy to find and collect, but one concern is that gross fecal analysis (GFA) techniques exaggerate the importance of small-bodied prey to mammalian mesopredator diets. To capitalize on the benefits of scat, we suggest the analysis of scat carbon and nitrogen isotope values (δ(13)C and δ(15)N). This technique offers researchers a non-invasive method to gather short-term dietary information. We conducted three interrelated studies to validate the use of isotopic values from coyote scat: 1) we determined tissue-to-tissue apparent C and N isotope enrichment factors (ε(13)* and ε(15)*) for coyotes from road kill animals (n = 4); 2) we derived diet-to-scat isotope discrimination factors for coyotes; and 3) we used field collected coyote scats (n = 12) to compare estimates of coyote dietary proportions from stable isotope mixing models with estimates from two GFA techniques. Scat consistently had the lowest δ(13)C and δ(15)N values among the tissues sampled. We derived a diet-to-scat Δ(13)C value of -1.5‰ ± 1.6‰ and Δ(15)N value of 2.3‰ ± 1.3‰ for coyotes. Coyote scat δ(13)C and δ(15)N values adjusted for discrimination consistently plot within the isotopic mixing space created by known dietary items. In comparison with GFA results, we found that mixing model estimates of coyote dietary proportions de-emphasize the importance of small-bodied prey. Coyote scat δ(13)C and δ(15)N values therefore offer a relatively quick and non-invasive way to gain accurate dietary information.